Computed tomography (CT) is a mature imaging technique that involves reconstruction of 2D cross sectional images of a 3D object using projection data. CT has a wide range of applications in medical imaging as a diagnostic tool, of which the first important example is X-ray tomography.
X-ray CT has a wide range of applications as a diagnostic tool in such disciplines as medicine, geology, anthropology and engineering science for visualizing the interior structure of solid objects. Of all the diagnostic tools, namely transmission tomography (X-ray), emission tomography (radioactive isotopes), ultrasound and magnetic resonance, X-ray CT was the first tool that revolutionized diagnostic medicine. Even though the mathematical foundation of image reconstruction from tomographic projection was first laid in 1917, avid interest in tomographic reconstruction began only after the invention of the X-ray tomography scanner in 1972. Since then several advances have been made resulting in fast and efficient data collection and reconstruction algorithms.
Over the past three decades, CT has evolved into a key diagnostic tool with a myriad of applications. Based on scanning configuration, motion, beam geometry and detector arrangements; several generations of CT scanners have evolved. Current CT scanners are often referred to as 3rd, 4th or 5th generation systems. The CT scanners to date have used parallel, fan or cone beam sources with translate/rotate, rotate/rotate, rotate-stationary and stationary-stationary (source and detectors are fixed on a circular array) scan configurations for projection measurements. All these scan geometries require precise positioning and alignment of the source-detector pairs. In some applications, the geometry of the object under diagnosis limits the scanning angle to less than 180 or 360 degrees, thereby affecting the quality of the reconstructed two dimensional cross sections. Besides these experimental and algorithmic limitations, the closed chamber of the CT scan equipment induces discomfort in claustrophobic patients and children.
Additionally, the increased level of terrorist activities has elevated the need for efficient screening of cargo containers and vehicles at ports of entry for the detection of contraband goods, collection of duties and minimizing illegal activities. It is desirable for any viable screening technique to be nondestructive, be non-intrusive (i.e., allowing inspection of sealed containers), yield high resolution images, and possess high sensitivity for contraband goods. X-ray CT has a wide range of applications as a diagnostic tool for visualizing the interior structure of solid objects. High energy X-rays (2-12 MeV) can penetrate large, high density objects and objects with a high atomic number. Such materials are often used for packaging contraband freight. At high energy, X-rays can penetrate steel walls that are ˜400 mm thick and offer excellent resolution ˜5 mm. Although high energy CT is a promising imaging modality for border security applications, its use has been prevented by the difficulty associated with rotating the detector/source pair around the test object. Consequently, most cargo inspection systems rely on simple systems that can provide only 2D projection images. Such images are difficult to interpret and it is often possible to hide contraband goods behind other benign looking objects. A missed detection due to poor resolution in the reconstructed image may lead to a breach of national security or contribute to illegal trafficking of drugs and weapons.
Accordingly, an apparatus is desired having the aforementioned advantages and solving and/or making improvements on the aforementioned disadvantages.